5.1 Conclusion
The escalation in flood frequency and intensity, attributed to the global rise in average temperatures driven by climate change, has thrust flood risk management into the forefront of our concerns. This study is a direct response to this pressing issue, focusing on the comprehensive evaluation of flood risk at the intersection of the national road N2 with Wadi Sefrou, situated to the south of Bni Drar city.
This region has encountered recurrent episodes of flooding, leading to extensive damage to infrastructure and properties in close proximity to the Wadi Sefrou watercourse. This watercourse is prominently delineated in the upper reaches of the plain but gradually dissipates towards the middle, branching into smaller streams. The repercussions of this wadi's flooding are felt downstream, inundating the plain.
Our approach relies on the utilization of the ArcGIS geographic information system, enabling the creation of a digital terrain model for the study area. This model incorporates watershed delineation and hydrographic network treatment. Additionally, a hydrological model is meticulously developed, coupling HEC-HMS with IBER to simulate runoff. These
cutting-edge technological tools have gained widespread recognition globally, serving as robust analytical instruments for the prediction of watershed hydrological behavior during flood events.
The results obtained from our study underscore the considerable vulnerability of the national road N2 at its intersection with Wadi Sefrou. Indeed, the maximum water depth in this zone is 2.7 meters for a 100-year return period, with a maximum flow velocity of 2 meters per second. Consequently, the road's infrastructure faces a high risk of damage, with the potential for traffic disruption. Notably, the national road N2 serves as a vital transport artery for this region, it links the region's principal cities to the city of Oujda, capital of the oriental region, and to the international airport of Angad, accommodating an median daily traffic volume surpassing 18,000 vehicles, according to data from the Ministry of Equipment and Water.
Furthermore, the consequences of flooding extend to residential areas in the downstream plain, situated to the south of Bni Drar's urban center, posing significant threats to the safety of residents and their property within this flood-prone zone.
The study extends its impact by mapping the extent of flooding, generating detailed maps depicting water depth, flow velocity, and flood hazard categorization. The findings of the visit made to the study area the day after the rainfall on September 02, 2023 confirmed that the results obtained are plausible and significant.
Our primary objective is to make substantive contributions to flood risk mitigation and the enhancement of territorial resilience.
5.2 Recommendations
To prevent the risk of flooding, we advocate a holistic approach that includes the application of flood hazard prevention strategies, the widespread dissemination of urbanization suitability maps, the establishment of a geographical information system (GIS) for flood risk assessment, coupled with an efficient warning system, and fostering a culture of prevention within civil society.
We also propose the implementation of nature-based solutions (NBS) to reduce the impact of flood risks. Indeed, researchers have recently been paying increasing attention to nature-based solutions (NBS), which can provide effective, sustainable, and cost-efficient solutions to mitigate flood risks (Jessica Penny and al.2023; Keiko Hori et al.2023). Nature-based solutions can help mitigate flood risks by restoring the hydrological functions of ecosystems.
Nature-based solutions focus on protecting, sustainably managing and restoring natural and modified ecosystems, effectively and appropriately adapted to the local context, while benefiting both biodiversity and human well-being.
The following are some nature-based solutions that can be used for flood risk management in our case:
1. The green approach: it consists of reforestation and afforestation wich are nature-based solutions for flood risk management. Planting trees and restoring forest cover can help to reduce the runoff and soil erosion, regulate water flow, and improve soil structure. Reforestation can also provide other benefits such as carbon sequestration, biodiversity conservation, and livelihood improvement
2. Retention basin: This is an open-air rainwater storage basin. It is designed to temporarily store rainwater before discharging it at a controlled rate into a watercourse or reusing it for irrigation.
3. Earth embankments: a linear earthen structure, raised above the natural ground level, which protects against flooding of watercourses. it also guides the flow of water towards the outlet.
4. Regular cleaning of hydraulic structures under the RN2: This operation is essential to prevent clogging of these structures by sediment and detritus transported during floods, and to maintain their drainage capacity as well as the preservation of the environment.
The map in Figure 12 shows a typical schematic plan of NBS solutions proposed in the study area to mitigate flood risk.